Interpretive Summary: Nanocomposites produced from incorporating a small amount of nanoclay into polymers have exhibited large improvements in barrier, mechanical, and heat resistant properties. In this study, we examined the effects of adding various nanoclays to wheat, corn, potato, and waxy corn starches. In particular, we focused on characterizing the rheological properties of the starch-nanoclay samples before and during gelatinization. These rheological properties provide insight into starch-clay interactions as well as the sample's viscoelastic behavior, which aid in improving sample processing. We found that wheat starch samples containing the most hydrophilic nanoclay, Cloisite Na+, displayed the largest elastic modulus before and during gelatinization. This indicated that Cloisite Na+ had more interactions with wheat starch than other nanoclays. In fact, x-ray diffraction results indicated that the Cloisite Na+ clays became intercalated during gelatinization. We then added Cloisite Na+ to corn, potato, and waxy corn starch and monitored their rheological properties during gelatinization. Wheat and corn starch had comparable elastic modulus values over the temperature range, whereas potato and waxy corn starch had elastic modulus values that decreased rapidly at high temperatures.

Technical Abstract:
The effects of incorporating various montmorillonite nanoclays to wheat, potato, corn, and waxy corn starch were examined by rheology and x-ray diffraction. The nanoclays included the hydrophilic Cloisite Na+ clay as well as the more hydrophobic Cloisite 30B, 10A, and 15A clays. Frequency sweep and creep results for wheat starch-nanoclay samples at room temperature indicated that the Cloisite Na+ samples formed more gel-like materials than the other nanoclay samples. X-ray diffraction results showed no intercalation of Cloisite Na+ clays at room temperature, suggesting that starch granules interacted only with the clay surface and not the interlayer. When the various wheat starch-nanoclay samples were heated to 95°C, the Cloisite Na+ samples exhibited a large increase in modulus. In contrast, the more hydrophobic nanoclay samples had comparable modulus values to the neat starch sample. These results suggested that during gelatinization, the leached amylose interacted with the Cloisite Na+ interlayer, producing better reinforcement and higher modulus values. X-ray diffraction results supported this interpretation since the data showed intercalation of Cloisite Na+ clay in the gelatinized samples. The samples containing wheat and corn starch showed comparable elastic modulus values during gelatinization. However, the potato and waxy corn samples had modulus values that rapidly decreased at higher temperatures.